1. Field of the Invention
The present invention relates to a method of forming an organic semiconductor layer pattern, and more particularly, to a method of forming an organic semiconductor pattern that can be used in the manufacture of various devices including display devices such as organic light emitting diodes (OLEDs), organic thin film transistors (OTFTs), etc.
2. Description of the Related Art
Recently, various flat display devices that can overcome drawbacks of cathode ray tubes, i.e., heavy weight and large volume, have been developed. Presently available flat display devices include plasma display panels (PDPs), liquid crystal displays (LCDs), field emission displays (FEDs), etc.
PDPs, among these flat display devices, are lightweight, thin and small and can be manufactured through simple processes and thus are drawing attention as the most suitable display for large screen display. However, PDPs also have drawbacks of low light-emitting efficiency, low brightness, and high power consumption. Contrary to this, although active matrix LCDs in which thin film transistors are used as switching devices are difficult to be used for large screen display because semiconductor manufacturing processes are used to manufacture the active matrix LCDs, the demand for the active matrix LCDs are increasing due to its use as display devices for laptop computers. However, LCDs have drawbacks such as high power consumption due to the use of a backlight unit. In addition, LCDs lead to a lot of light loss due to the use of optical devices such as a polarizing filter, a prism sheet, and a diffusion plate, etc. and have a small viewing angle.
A new display market trend in the information society will be lead by displays such as paper-like flexible displays, which can provide high quality display and pursuit user's convenience in the mobile field. In order to implement such displays, flexible and durable active driving devices should be made with low-cost processes that can be easily applied to develop active driving device arrays.
In the development of such flexible display devices, a patterning process using an organic semiconductor material is one of the important fields involved. Since the development of polyacetylene that is a conjugated organic polymer having semiconductor characteristics, due to the advantages of organic materials such as the diversity of synthesis methods thereof, the ability to be easily molded in fiber or film form, flexibility, conductivity, low-production cost, etc., research into organic semiconductors as new electric and electronic materials has been intensively performed in various fields, for example, in the functional electronic device field, optical device field, etc.
Processes using an organic semiconductor material can be roughly classified into polymer semiconductor processes and organic semiconductor processes. In polymer semiconductor processes, polymer is used as a semiconductor material. In particular, a polymer semiconductor process is a technique including dissolving a polymer material in a solvent, coating the resultant solution on a substrate using, for example, spin coating, evaporating the solvent, and patterning the coated film. Meanwhile, an organic semiconductor process is a process using a low-molecular weight organic material, not polymer, and includes a patterning process using, in most cases, vacuum deposition. Pentacene is a representative low-molecular weight organic material.
For a monochromic device, organic light-emitting diodes using polymer can be simply manufactured using a spin-coating process and have a low driving voltage. However, the organic light emitting diodes using polymer have a low luminous efficiency and short lifetime. For a full-color device, polymer patterning is performed using an inkjet technique or a laser transfer technique to obtain red, green, and blue patterns. However, luminance characteristics such as efficiency, lifetime, etc., have to be optimized when applying an inkjet technique or a laser transfer technique. Especially, when using a laser transfer technique, most single polymeric materials are not easily transferred.
A low-molecular weight organic semiconductor such as pentacene hardly dissolves in a solvent and thus cannot be coated in film form. For this reason, when forming a pattern of such a low-molecular weight organic semiconductor on a substrate, a shadow mask method is used in most cases. In the shadow mask method, deposition is performed with a patterned shadow mask disposed adjacent to the substrate. The method of using a shadow mask is advantageous in that there is no need to perform a lithography process but has the following problems.
In particular, the shadow mask has to be thin enough to form a fine pattern therein. Accordingly, it is difficult to handle the shadow mask. In addition, the shadow mask is expensive and cannot be unlimitedly used since the shadow mask is disposed very close to the substrate on which a pattern will be formed. Furthermore, the radiation heat generated by a device used to heat a deposited material expands the shadow mask, thereby causing sagging of a center portion of the shadow mask. The sagging of the shadow mask become more serious as a larger substrate is used, thereby blocking the manufacture of high-definition, large-screen displays.
Therefore, there is an increasing need for a method of patterning a low-molecular weight material such as pentacene, not through deposition. Furthermore, if patterning can be performed at a temperature lower than a temperature required for deposition, it would be very attractive to manufacture future-oriented displays, etc.